Use of polysilazane for the production of hydrophobically and oleophobically modified surfaces

ABSTRACT

The invention relates to the use of a polysilazane solution which comprises a polysilazane of the formula 1  
                 
where n has been adjusted so that the polysilazane has a number-average molar mass of from 150 to 150 000 g/mol, and also comprises a solvent and a catalyst, as a primer for the coating of a surface with fluorosilanes or with fluorine-containing condensates.

The present invention relates to a process for producing surfaces withhydrophobic and oleophobic properties using polysilazane as a primercoating for subsequent application of fluorine-containing components.

On surfaces with hydrophobic and oleophobic properties, oil-soluble andwater-soluble contamination has poor adhesion and can readily be removedby water and mild cleaning compositions. Furthermore, on surfaces withhydrophobic and oleophobic properties water forms droplets with largecontact angles, which run off without leaving any lime spots. Veryrecently, these easy-clean coating systems have also been utilizedcommercially.

Easy-clean coatings are usually not self-cleaning, but reduce theadhesion of dirt and make the surface easier to clean. They contributeto conservation of the environment, because there is no need to useaggressive cleaning compositions, and instead of these it is possible touse mild and neutral cleaning compositions. Measurement of the contactangle has become generally accepted as a measure of easy-cleanproperties. The higher the contact angle of a water droplet with respectto the surface, the greater is the run-off effect for water droplets,and the smaller the extent of formation of lime spots.

U.S. Pat. No. 5,997,943 describes the use of fluorosilanes(fluorine-containing alkoxysilanes) on glass in mixtures with organicsolvents, acids, and water. The fluorosilanes described are mixed withother organosilanes and dissolved in suitable solvents. Addition ofacids, such as acetic acid or sulfuric acid, activates the hydrolysis ofthe silanes. Once this solution is applied to the silicatic surface, thesilanes react with the surface and become covalently bonded. Thiscoating increases the contact angle of the water droplets on the glasssurface from usually 50-60° to 100-110°. By way of example, typicalfluorosilanes are C₆F₁₃-alkylethyltriethoxysilane,C₈F₁₇-alkylethyltriethoxysilane, C₁₀F₂₁-alkylethyltriethoxysilane andC₁₂F₂₅-alkylethyltriethoxysilane, and the corresponding methoxy,propoxy, butoxy, and methoxyethoxy, methoxydiethoxy and methoxytriethoxycompounds.

The perfluoroalkyl groups increase the contact angle of water and ofhydrocarbons on the coated surface, and reduce the adhesion of organicand inorganic contamination, for example of fats, lime, and lime soaps.Fluorosilanes are suitable easy-clean coating compositions on silicaticsurfaces.

EP-A-0 846 715 describes the preparation of fluorine-containingcondensates from perfluoroalkylethyltrialkoxysilanes, using organicacids as hydrolysis catalyst. In that laid-open specification,fluorine-containing condensates are prepared by partial condensation ofperfluoroalkylethyltrialkoxysilanes. For this, the fluorosilanesdescribed above and other organosilanes are hydrolyzed using asubstoichiometric amount of water, through acidification with aceticacid, sulfuric acid, or hydrochloric acid, thus givingfluorine-containing condensates colloidally dispersed in a solvent, suchas ethanol or isopropanol. Fluorine-containing condensates can likewisebe used for the coating of silicatic surfaces. Once the solvent(ethanol, isopropanol) has vaporized, the fluorine-containingcondensates react with the surface and form covalent bonds. Thefluorine-containing condensates are suitable for easy-clean coatings,and exhibit higher storage stability than solutions of fluorosilanes,and the coating also has higher resistance to scrubbing and washing.

EP-A-0 846 716 describes the combination of fluorosilanes with otherorganosilanes for preparing organopolysiloxanes in solvent mixturescomposed of water and alcohols.

If silicatic surfaces, such as glass and ceramics, or surfaces composedof metal oxides, are coated with fluorosilanes or withfluorine-containing condensates, these react with the oxides of thesurface and become covalently bonded. The chemical bonding between thesubstrate and the fluorosilane or fluorine-containing condensate durablysecures the hydrophobic and oleophobic fluorine-containing substituentson the surface, and their effects are retained.

A disadvantage is that fluorosilanes or fluorine-containing condensatesdo not react with surfaces which do not have oxide groups or hydroxidegroups. For example, metals, plastics, paints, and resins cannot beprovided with a permanent hydrophobic and oleophobic effect with the aidof fluorosilanes or of fluorine-containing condensates.

Another disadvantage is the relatively small particle size of thefluorosilanes or fluorine-containing condensates. On highly absorbentsurfaces or surfaces with large pores, the fluorosilanes orfluorine-containing condensates diffuse into the substrate and do notprovide a sufficient easy-clean covering on the surface.

It is an object of the present invention to develop a process whichpermits permanent hydrophobic and oleophobic properties to be providedon metals, plastics, paints, resins, and porous surfaces.

Surprisingly, it has now been found that porous surfaces can be providedwith permanent hydrophobic and oleophobic properties by pretreatmentwith polysilazane solutions.

The invention provides the use of a polysilazane solution whichcomprises a polysilazane of the formula 1

where n has been adjusted so that the polysilazane has a number-averagemolar mass of from 150 to 150 000 g/mol, and also comprises a solventand a catalyst, as a primer for the coating of a surface withfluorosilanes or with fluorine-containing condensates.

The invention further provides a process for producing a surface coatedwith fluorosilanes or with fluorine-containing condensates, by, in afirst step, bringing the uncoated surface into contact with acomposition which comprises a polysilazane of the formula 1 andcomprises a solvent and a catalyst, and then, in a second step, bringingthe surface obtained in the first step in contact with fluorosilanes orwith fluorine-containing condensates. It is preferable for the solventto be permitted to vaporize after the first step.

The invention further provides a coated surface obtainable by theprocess described above.

The molar mass of the polysilazane is preferably from 300 to 10 000g/mol, in particular from 600 to 3 000 g/mol.

The polysilazane solution preferably comprises, based on the weight ofthe solution, from 0.001 to 35% by weight, in particular from 0.5 to 5%by weight, and specifically from 1 to 3% by weight, of the polysilazane,from 0.00004 to 3.5% by weight, in particular from 0.02 to 0.5% byweight, and specifically from 0.04 to 0.3% by weight, of the catalyst,and solvent to 100% by weight.

Catalysts permit the conversion of polysilazane into silicon dioxide atlow temperatures, in particular at room temperature. The amountspreferably used of the catalyst are from 0.1 to 10%, based on the weightof the polysilazane.

Suitable catalysts are N-heterocyclic compounds, such as1-methylpiperazine, 1-methylpiperidine, 4,4′-trimethylenedipiperidine,4,4′-trimethylenebis(1-methylpiperidine), diazobicyclo[2.2.2]octane,cis-2,6-dimethylpiperazine.

Other suitable catalysts are mono-, di-, and trialkylamines, such asmethylamine, dimethylamine, trimethylamine, phenylamine, diphenylamineand triphenylamine, DBU (1,8-diazabicyclo[5.4.0]-7-undecene), DBN(1,5-diazabicyclo[4.3.0]-5-nonene), 1,5,9-triazacyclododecane and1,4,7-triazacyclononane.

Other suitable catalysts are organic or inorganic acids, such as aceticacid, propionic acid, butyric acid, valeric acid, maleic acid, stearicacid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid,chloric acid, and hypochlorous acid.

Other suitable catalysts are metal carboxylates of the formula(RCOO)_(n)M of saturated or unsaturated, aliphatic or alicyclic C₁-C₂₂carboxylic acids, and metal ions, such as Ni, Ti, Pt, Rh, Co, Fe, Ru,Os, Pd, Ir, and Al; n is the charge on the metal ion.

Other suitable catalysts are acetylacetonate complexes of metal ions,such as Ni, Pt, Pd, Al, and Rh.

Other suitable catalysts are metal powders, such as Au, Ag, Pd, or Niwith a particle size of from 20 to 500 nm.

Other suitable catalysts are peroxides, such as hydrogen peroxide, metalchlorides, and organometallic compounds, such as ferrocenes, andzirconocenes.

The solvent permits the preparation of solutions of the polysilazane andof the catalyst with sufficiently long storage time without formation ofsilanes, hydrogen, or ammonia. Suitable solvents are aromatic, cyclic,and aliphatic hydrocarbons, halogenated hydrocarbons, and ethers.

By way of example, suitable solvents are aliphatic, aromatic, and cyclichydrocarbons, and dibutyl ether.

The polysilazane solution described may be used to coat a wide selectionof substrate surfaces. Suitable substrates are

-   -   metals, e.g. iron, stainless steel, zinc, aluminum, nickel,        copper, magnesium, and their alloys, silver, and gold,    -   plastics, e.g. polymethyl methacrylate, polyurethane,        polycarbonate, polyesters, such as polyethylene terephthalate,        polyimides, polyamides, epoxy resins, ABS, polyethylene,        polypropylene, polyoxymethylene,    -   porous mineral materials, such as concrete, fired clay, marble,        basalt, asphalt, loam, terracotta,    -   paint surfaces, e.g. polymer-based emulsion paints, acrylic        paints, epoxy paints, melamine resins, polyurethane resins, and        alkyd paints, and    -   organic materials, such as wood, leather, parchment, paper, and        textiles.

To accelerate the process, in one preferred embodiment the polysilazanesolution may be applied with an aqueous surfactant solution. Preferredsurfactants are alkanesulfonates, betaines, alkyl ethoxylates, and ethersulfates. The surfactant solution preferably comprises from 0.1 to 5% ofsurfactants, and is applied to the polysilazane-coated surface either byimmersion or by wiping or spraying.

The reaction of perfluoroalkyl-containing compounds with the surfaceobtained in the first step of the process provides hydrophobic andoleophobic properties, and easy-clean properties. The contact angle ofdistilled water then achieves values >90°, in particular >110°. By wayof example, perfluoroalkyl-containing compounds areC₆F₁₃-alkylethyltriethoxysilane, C₈F₁₇-alkylethyltriethoxysilane,C₁₀F₂₁-alkylethyltriethoxysilane, and C₁₂F₂₅-alkylethyltriethoxysilane,and the corresponding methoxy, propoxy, butoxy, and methoxyethoxy,methoxydiethoxy, and methoxytriethoxy compounds, and fluorine-containingcondensates.

The result is that permanent easy-clean properties are readilyavailable, even on substrates which hitherto could not be provided withthese properties in this way. It is also advantageously possible to sealhighly absorbent and porous substrates with the aid of the polysilazanecoating.

Suitable solvents are mono- and polyalkylene glycol dialkyl ethers(glymes), or mixtures composed of mono- and polyalkylene glycol dialkylethers with aliphatic, cyclic, or aromatic hydrocarbons.

For the purposes of this invention, vapor pressure osmometry is used todetermine the molar mass of the polysilazane.

EXAMPLES Examples of the composition of suitable polysilazane solutionsare given below (data in % by weight):

Solution 1

20% of polysilazane with an average molar mass of 2 000 g/mol

0.8% of 4,4′-trimethylenebis(1-methylpiperidine)

79.2% of xylene

Solution 2

5% of polysilazane with an average molar mass of 2 000 g/mol

0.2% of 4,4′-trimethylenebis(1-methylpiperidine)

19.8% of xylene

75% of hydrocarbon mixture comprising aromatics (®Pagasol AN 45 fromExxonMobil)

Solution 3

1% of polysilazane with an average molar mass of 2 000 g/mol

0.04% of 4,4′-trimethylenebis(1-methylpiperidine)

3.96% of xylene

95% of hydrocarbon mixture comprising aromatics (®Pagasol AN 45 fromExxonMobil)

Solution 4

5% of polysilazane with an average molar mass of 2 000 g/mol

0.2% of 4,4′-trimethylenebis(1-methylpiperidine)

19.2% of xylene

75% of hydrocarbon mixture comprising aromatics (®Varsol 40 fromExxonMobil)

Solution 5

1% of polysilazane with an average molar mass of 2 000 g/mol

0.04% of 4,4′-trimethylenebis(1-methylpiperidine)

3.96% of xylene

95% of hydrocarbon mixture comprising aromatics (®Varsol 40 fromExxonMobil)

Solution 6

5% of polysilazane with an average molar mass of 2 000 g/mol

0.2% of 4,4′-trimethylenebis(1-methylpiperidine)

19.8% of xylene

75% of dipropylene glycol dimethyl ether

Solution 7

1% of polysilazane with an average molar mass of 2 000 g/mol

0.04% of 4,4′-trimethylenebis(1-methylpiperidine)

3.96% of xylene

95% of dipropylene glycol dimethyl ether

Solution 8

5% of polysilazane with an average molar mass of 2 000 g/mol

0.2% of 4,4′-trimethylenebis(1-methylpiperidine)

19.8% of xylene

20% of dipropylene glycol dimethyl ether

55% of hydrocarbon mixture low in aromatics (Exxsol D 40 fromExxonMobil)

Solution 9

1% of polysilazane with an average molar mass of 2 000 g/mol

0.04% of 4,4′-trimethylenebis(1-methylpiperidine)

3.96% of xylene

20% of dipropylene glycol dimethyl ether

75% of hydrocarbon mixture low in aromatics (Exxsol D 40 fromExxonMobil)

Solution 10

0.2% of polysilazane with an average molar mass of 2 000 g/mol

0.008% of 4,4′-trimethylenebis(1-methylpiperidine)

0.792% of xylene

20% of dipropylene glycol dimethyl ether

79% of hydrocarbon mixture low in aromatics (Exxsol D 40 fromExxonMobil)

The following examples below are intended to provide further descriptionof the use of a polysilazane solution for primer-coating and thesubsequent application of fluorine-containing components.

Example 1 Easy-Clean Coating of Steel Sheet

A non-rusting steel sheet was coated with a 1% strength polysilazanesolution (solution 3), using a nonwoven viscose cloth to distributeabout 8 ml/m² of the solution uniformly on the surface, until thesolvent has vaporized. Application of the polysilazane solution wasrepeated once. The polysilazane-coated steel sheet was then coated withan aqueous solution of a fluorine-containing condensate (®Nano-E2C 200from Nanogate, Saarbrücken). The amount applied was 8 ml/m², applicationbeing uniform by manual distribution, using a nonwoven viscose cloth.For condensation of the fluorine-containing condensate, the steel sheetis cured at 260° C. for 1 hour. The contact angle of distilled water was74° prior to coating and 110° after coating.

In a second experiment, the polysilazane-coated steel sheet was treatedwith an aqueous surfactant solution. The wetting promoter used toprepare the aqueous surfactant solution had the following composition:®Hostapur SAS 30 28%  ®Genagen CA 050 3.6%   ®Genapol UD 080 5%Propylene glycol 3% Sodium benzoate 0.3%   Citric acid for adjustment topH 6 Demineralized water remainder

2 ml/l of the wetting promoter were dissolved in water to prepare thesurfactant solution. The surfactant solution was applied to thepolysilazane-coated steel sheet, then rinsed with demineralized water,and dried. The solution of the fluorine-containing condensate inisopropanol®Nano-E2C 110 from Nanogate, Saarbrücken), was applied to thedry steel sheet, twice distributing 8 ml/m² uniformly on the surface,using a nonwoven viscose cloth, until the isopropanol had vaporized. Thefluorine-containing condensate cured at room temperature and becomepermanently bonded to the steel sheet. The contact angle of distilledwater after coating was 109°.

Example 2 Easy-Clean Coating of Zinc Sheets

A zinc sheet was twice coated manually as described in example 1 with a1% strength solution of polysilazane (solution 3). 8 ml/m² of thefluorine-containing condensate in isopropanol (®Nano-E2C 110 fromNanogate, Saarbrücken) were then applied twice and cured at roomtemperature. The hydrophobic and oleophobic coating could be bondedpermanently to the zinc sheet. The contact angle of distilled water was63° prior to coating with polysilazane and 108° after coating with thefluorine-containing condensate.

Example 3 Easy-Clean Coating of Polycarbonate Sheets

Polycarbonate sheets of thickness 2 mm were coated twice with a 1%strength polysilazane solution (solution 3). For this, 8 m/m² weredistributed, using a nonwoven viscose cloth, until the solventevaporated. This was followed by coating twice with 8 ml/m² of thefluorine-containing condensate in isopropanol (®Nano-E2C 110 fromNanogate, Saarbrücken). This was likewise applied using a nonwovenviscose cloth until the isopropanol vaporized. Curing took place at roomtemperature. The contact angle of distilled water was 76° prior tocoating with polysilazane and 115° after coating with thefluorine-containing condensate.

Example 4 Easy-Clean Coating of Polyethylene Terephthalate

PET film was coated twice with a 1% strength polysilazane solution(solution 3). For this, 8 ml/m² were distributed, using a nonwovenviscose cloth, until the solvent vaporized. This was followed by coatingtwice with 8 ml/m² of the fluorine-containing condensate in isopropanol(®Nano-E2C 110 from Nanogate, Saarbrücken). This was likewise appliedusing a nonwoven viscose cloth until the isopropanol vaporized.

Curing took place at room temperature. The contact angle of distilledwater was 17° prior to coating with polysilazane and 115° after coatingwith the fluorine-containing condensate.

Example 5 Easy-Clean Coating of Automotive Paints

An automotive paint was twice coated with a 1% strength polysilazanesolution (solution 3). For this, on each occasion 8 ml/m² weredistributed, using a nonwoven viscose cloth, until the solventvaporized. This was followed by two applications of 8 ml/m² of thefluorine-containing condensate in isopropanol (®Nano-E2C 110 fromNanogate, Saarbrücken). A nonwoven viscose cloth was used forapplication until the isopropanol vaporized. After coating, the surfaceis markedly hydrophobic. Water droplets rapidly run off.

Example 6 Easy-Clean Coating of Brass

A brass sheet was twice coated with a 1% strength polysilazane solution(solution 3). Consumption was 8 ml/m² per coating step. After 10minutes, the polysilazane layer was treated with an aqueous surfactantsolution from example 1 and converted to silicon dioxide. This wasfollowed by two applications of 8 ml/m² of the fluorine-containingcondensate in isopropanol (Nano-E2C 110 from Nanogate, Saarbrücken). Thecontact angle of distilled water was 78° prior to polysilazane coating.After coating with the fluorine-containing condensate the contact anglewas 115°.

In another variant, a fluorosilane solution in isopropanol and water wasused to confer hydrophobic and oleophobic properties. For this, thefollowing solution was provided: 2% ofC₆-perfluoroalkylethyltriethoxysilane 88% of isopropanol 0.6% of glacialacetic acid 9.4% of demineralized water

The polysilazane-coated brass sheet was twice coated with 8 ml/m² ofthis fluorosilane solution. The solution was uniformly distributedmanually, using a nonwoven viscose cloth, until the volatileconstituents have vaporized. The contact angle of distilled water afterfluorosilane coating was 124°.

Example 7 Easy-Clean Coating of Copper Sheets

A copper sheet was coated as in example 6 with polysilazane, and treatedwith the aqueous surfactant solution from example 1 for conversion tosilicon dioxide. This was followed by two applications of 8 ml/m² of thefluorine-containing condensate in isopropanol (®Nano-E2C 110 fromNanogate, Saarbrücken). The contact angle of distilled water was 82°prior to polysilazane coating. After coating with thefluorine-containing condensate the contact angle was 114°. As analternative to the fluorine-containing condensate, use was made of thesolution, described in example 6, of theC₆-perfluoroalkylethyltriethoxysilane in isopropanol/water for coating.After two applications of 8 ml/m² of the fluorosilane solution, thecontact angle measured for distilled water was 125°.

Example 8 Easy-Clean Coating of Stainless Steel Sheets

A stainless steel sheet was coated as in example 6 with polysilazane,and treated with the aqueous surfactant solution from example 1 forconversion to silicon dioxide. This was followed by two applications of8 ml/m² of the fluorine-containing condensate in isopropanol (®Nano-E2C110 from Nanogate, Saarbrücken). The contact angle of distilled waterwas 730 prior to polysilazane coating. After coating with thefluorine-containing condensate the contact angle was 108°. As analternative to the fluorine-containing condensate, use was made of thesolution, described in example 6, of theC₆-perfluoroalkylethyltriethoxysilane in isopropanol/water forhydrophobic and oleophobic coating. After two applications of 8 ml/m² ofthe fluorosilane solution, the contact angle measured for distilledwater was 115°.

Example 9 Easy-Clean Coating of Aluminum Sheets

An aluminum sheet was coated as in example 6 with polysilazane, andtreated with the aqueous surfactant solution from example 1 forconversion to silicon dioxide. This was followed by two applications of8 ml/m² of the fluorine-containing condensate in isopropanol (®Nano-E2C110 from Nanogate, Saarbrücken). The contact angle of distilled waterwas 78° prior to polysilazane coating. After coating with thefluorine-containing condensate the contact angle was 112°. As analternative to the fluorine-containing condensate, use was made of thesolution, described in example 6, of theC₆-perfluoroalkylethyltriethoxysilane in isopropanol/water forhydrophobic and oleophobic coating. After two applications of 8 ml/m² ofthe fluorosilane solution, the contact angle measured for distilledwater was 120°.

Example 10 Easy-Clean Coating of Polypropylene, Melamine-Resin-CoatedParticle Board, and Laminated Floorcovering

A polypropylene sheet, a melamine-resin-coated particle board and alaminated floorcovering sheet were coated, as in example 6, withpolysilazane. This was followed by two applications of 8 ml/m² of thefluorine-containing condensate in isopropanol (®Nano-E2C 110 fromNanogate, Saarbrücken). As an alternative to the fluorine-containingcondensate, use was made of the fluorosilane solution described inexample 6 for hydrophobic and oleophobic coating, 8 ml/m² being appliedtwice. The following contact angles were measured for distilled water.

Polypropylene

Prior to polysilazane coating: 100°

After coating with the fluorine-containing condensate: 112°

After coating with the fluorosilane solution: 128°

Melamine-resin-coated particle board

Prior to polysilazane coating: 77°

After coating with the fluorine-containing condensate: 127°

After coating with the fluorosilane solution: 122°

Laminated floorcovering

Prior to polysilazane coating: 40°

After coating with the fluorine-containing condensate: 115°

After coating with the fluorosilane solution: 122°

Example 11 Easy-Clean Coating of Polycarbonate Wheel Caps

As described in example 6, polycarbonate wheel caps were twice coatedwith 8 ml/m² of the polysilazane solution (solution 3) and then treatedwith the aqueous surfactant solution from example 1. The polycarbonatewheel cap was then twice coated with 8 ml/m² of the fluorine-containingcondensate in isopropanol (Nano-E2C 110 from Nanogate, Saarbrücken). Asan alternative, 8 ml/m² of the fluorosilane solution from example 6 weretwice used for coating. The curvature of the wheel cap preventeddetermination of the contact angle. However, this surface is markedlyhydrophobic and water droplets readily ran off.

1. A process for coating a surface with fluorosilanes or fluorosilanecontaining condensates, said process comprising disposing on saidsurface a primer comprising fluorosilanes or fluorosilane containingcondensates and a polysilazane solution which comprises a polysilazaneof the formula 1

where n has been adjusted so that the polysilazane has a number-averagemolar mass of from 150 to 150 000 g/mol, and a solvent and a catalyst,and curing the primer to provide the coated surface.
 2. The process ofclaim 1, in which the polysilazane solution comprises from 0.001 to 35%by weight of the polysilazane.
 3. The process of claim 1, in which thecatalyst comprises from 0.00004 to 3.5% by weight of the polysilazanesolution.
 4. The process of claim 1, wherein the catalyst is selectedfrom the group consisting of N-heterocyclic compounds, mono-alkylamines,di-alkylamines, and trialkylamines, organic acids, inorganic acids,metal carboxylates of the formula (RCOO)_(n)M of saturated orunsaturated, aliphatic or alicyclic carboxylic acids where R=C₁-C₂₂, andmetal ions M with charge n, acetylacetonate complexes of metal ions,metal powders with a particle size of from 20 to 500 nm, peroxides,metal chlorides, organometallic compounds, and mixtures thereof.
 5. Theprocess of claim 1, in which the solvent is selected from the groupconsisting of aromatic hydrocarbons, cyclic hydrocarbons, and aliphatichydrocarbons, halogenated hydrocarbons, ethers, and mixtures thereof. 6.A process for producing a surface coated with fluorosilanes or withfluorine-containing condensates, by, in a first step, bringing theuncoated surface into contact with a composition which comprises apolysilazane of the formula 1, a solvent and a catalyst, and then, in asecond step, bringing the surface obtained in the first step in contactwith a fluorosilane compound or fluorine-containing condensate, andcuring the composition to provide said coated surface.
 7. The process asclaimed in claim 6, in which the fluorosilane compound orfluorine-containing condensate is a perfluoroalkyl-containing compoundselected from the group consisting of C₆F₁₃-alkylethyltriethoxysilane,C₈F₁₇-alkylethyltriethoxysilane, C₁₀F₂₁-alkylethyltriethoxysilane, andC₁₂F₂₅-alkylethyltriethoxysilane, the corresponding methoxy, propoxy,butoxy, methoxyethoxy, methoxydiethoxy, methoxytriethoxy compounds ofsaid silane compounds, and mixtures thereof.
 8. A coated surfaceobtained by the process of claim 6.